Temperature responsive devices



Sept. 19, 1961 w. H. FISHER 3,001,051

TEMPERATURE RESPONSIVE DEVICES Filed Jan. 18, 1960 & Fig.4

7 M L/F A JE/V E/16 INVEN YOK United States Patent 3,001,051 TEMPERATURE RESPONSIVE DEVICES William Hawarden Fisher, -Manchester, England, assignor to The General Electric Company Limited, London,

England Filed Jan. 18, 1960, Ser. No. 3,030 7 Claims priority, application Great Britain Jan. 16, 1959 7 Claims. (Cl. 200138) This invention relates to temperature responsive devices of the kind including a bi-metallic strip-like element arranged to deflect and arranged to operate under a compressive force applied along its length.

One object of the present invention is to provide a temperature responsive device having a novel and improved form of springing that gives a more positive action to the device than heretofore.

According to the present invention, in a temperature responsive device of the kind including a bi-metallic striplike element arranged to deflect and arranged to operate under acompressive force applied along its length, a U- shaped spring member spans the element and applies the said compressive force.

Means may be provided for adjusting the said force; these means may be arranged directly to alter the force applied by the spring member and also these means may be arranged directly to alter the force in the element itself.

The element may be fixed to supporting means at one end thereof, and at the other end may engage the spring member. These supporting means may comprise a carriage pivoted in the main body of the device on an axis transverse to the length of the spring member, the element beingattached to the carriage at a point remote from'the pivotal axis of the carriage and from the point where the spring member engages the element.

The spring member may engage knife edges on the parts with which it co-operates. One of these knife edges may be on a member of L form, the branch of the L bearing the knife edge being arranged to project through a hole in one end wall of the main body of the device to engage with the spring member, the other branch being adapted for adjustment towards or away from the -wall to alter the force applied by the spring member.

The other knife edge may be attached to the end of the element not attached to the carriage.

The means arranged directly to alter the force in the element itself may engage with the supporting means for the element, the pressure with which such engagement is made being variable and capable of adjustment dependent upon the force-desired in the element. These means may comprise a threaded rod passing through a threaded bush in the base of the device, the end of the rod bearing on the support means.

The end of the element not attached to the carriage may carry .an electric-a1 contact, the electrical contact being adapted to make and break contact with a second electrical contact.

In order that the invention may be clearly understood an electric thermostatic switch, for use as a room thermostat for controlling heating apparatus inthe room and incorporating a temperature responsive device in accordance with the present invention, will now be described by way of example with reference to the four figures of the accompanying drawing, in which FIGURE 1 shows a 7 top plan view of the switch, FIGURE 2 shows a sectional side elevation on the line II-II in FIGURE 1, FIG- URE 3 shows an end elevation of the switch in the direction of the arrow III in FIGURE 1, and FIGURE 4 shows a detail of support means used in the switch.

Referring now to the drawing and particularly to FIG- URES 1, 2 and 3 thereof, the electr switch comprises a Patented Sept. 19, 1961 e CU 2 main body 1 in the form of a channel section of mild steel having a moulded part 2 of insulating material attached to the base of the channel and attached to it by screws 3 passing through the main body 1 into the moulded part 2.

The moulded part 2 projects beyond one end of the main body 1 and to this projection is attacheda terminal assembly for the switch. The terminal assembly itself comprises a fixed contact 4 which is screwed to the part 2 and is adjustable in the part 2 by virtue of its threaded nature. A terminal connection is in electrical contact with the contact 4 and this connection comprises a part tubular member 5 attached to the part 2 by a screw 6, the solid part of the member 5 having a threaded hole into which and through which the contact 4 is screwed and passes into the part 2. The tubular part of the member 5 has a screw 8 located in one wall adapted to engage with electrical supply wires entered in the said tubular part and retain them positively in position.

The terminal assembly also includes a terminal block 9 having a hole 10 for receiving an electric supply Wire and a screw 11 for retaining such a wire in the terminal block. This terminal block 9 is connected to a moving contact 12 by means of a jumper strap 14 and this is attached to the block 9 by a'screw 15 which also retains the block 9 in attachment with the part 2.

()nesection of the moulded part 2 extends transversely to the general plane of the switch and this section has .attached to it an arm 16 carrying an adjustable back stop 17, which may include, in certain applications, a contact as well, which engages with the back of the movable,

contact 12 to limit its degree of movement.

The end of the main body 1 not carrying the terminal assembly has a metal end cap 18 fitted over it. There is provided in the end cap an aperture through which a knife edge member 19 passes. This is formed from an L-shaped piece of metal and while one branch of the L carrying the knife edge projects through the said aperture the other branch of the L has a threaded hole cut in it into which a screw 20 passes. The screw 20 also passes through an aperture in the end cap 18 of sufficient dimensions to allow the body of the screw to pass freely through while retaining the head of the screw on the outside of the end cap 18.

The side walls of the main body 1 each have a notch 21 cut in them, equally dimensioned and spaced from the capped end of the main body 1. This notch is best illustrated in FIGURE 4, to which figure reference is now made, and serves as a seating for a projection 22 on the walls of a channel shaped carriage member 23 supporting a bi-metallic element in the form of a strip 24.

Referring back now to FIGURES l, 2 and 3 the carriage member 23 consists of a channel of mild steel having the projections 22 on each of its side walls and situated externally at one end thereof. The bi-metallic strip 24 passes through the channel of the carriage 23 and is held at the end of the carriage remote from the projections 22 by rivets 25 and a clamping member 27. This clamping member 27 also secures one end of a resilient member 28 of spring metal, the other end of which engages with the end cap 18. It will be appreciated from the foregoing description that the carriage 23 is supported in the main body 1 by the projections 22 engaging in the notches 21 and through the resilient member 28 engaging with the end cap 18; the carriage 23 is therefore capable of limited movement by rotation of the projections 21 in the notches 22 against the resistance of the member 28.

The bi-metallic strip 24 passes along the length of the main body 1 from the point at which it is fixed to the carriage 23 and the end remote from the carriage is tapered and has attached to it by rivets 29 on its top side a steel knife edge 30 and on its underside, i.e. the side nearest the base of the channel of the main bodyl, a" plastic plate 31 which extends over the fixed contact 4 .strip 24 operates to open or close the contacts 4, 12.

The adjusting means comprises an internally'threaded bush 35 set in the main body 1 of the switch beneath the end. of the carriage 23 to which is attached the bimetallic strip 24. This bush 35 receives a threaded rod 36 having a rounded end 37 which bears on the underside of the carriage 23. The rod 36 is screwed into or out of the bush 35 and the rounded end 37 raises or lowers the end of the carriage 23 pivoting it aboutthe projections 22 and thereby altering the stressing of the bi-metallic "strip 24-. I A graduated dial 38 is attached to the rod 36 by means of a nut 40, and this dial 38 is calibrated with temperature settings so that any desired temperature of the switch within a specified range may easily *be preset. In order that the switch may operate with very light currents if necessary a heating resistor 41 is incorporated beneath the bi-me'tallic strip24 in the channel of the main body 1. One end of the resistor .41 is connected to a subsidiary terminal block 42 attached to the part 2 by a screw 43 which also acts to transfer current from the block 42to thelejad of the resistor 41. A lead 44 from the other end of the resistor 41 runs along the bottom of the channel of the main body 1 through a hole 45 in the part 2 and is attached to the tubular part 5. This means that the resistor is electrically connected to the Y fixed contact 4, and the arrangement is such that the resistor 41 is connected in parallel with the load by an extra wire from the neutral side of the circuit to the terminal block 42.

Theoperation of the switch is that when it .is set by means of the screw 20 and/or the temperature adjusting means comprised by the bush and the rod 36 to operate at a particular temperature, the operating temperature in this example being above the normal temperature, the contacts'4 and 12 are closed. When the bi metal strip 24 reaches the operating temperature it snaps up under the combined action of the thermal stresses set up in the bi-metal strip 24 itself and those produced by virtue of the force exerted upon it by the spring member '32 thus ensuring'a clear sharp break between the contacts 4, 12. When the temperature falls below the operating temperature the forces acting on the bi-metal stripv 24 are in draws the member 19 nearer 'to or further from the end caplS and in so doing alters the tension in the spring member 32 by the knife edge member 19 either forcing the two ends of the spring member further apart or closer together, the further apart they are meaning an increase in tension and greater forces being set up in the bi-metallic strip 24. The use of this method of adjust- I ment should be :a fone onlyilmethod andlonce the switch has been set to operaterover the required range the screw 20 can be sealed in position'with any suitable compound. The second temperature adjustment means comprised by the.rod136 and the bush 35 is the customers adjust- Due to the wide variety of quality of ment means. The action of the means is that as the rod 36 is screwed into the bush 35 the rounded end 37 bears on the underside of the carriage 23 and forces the end of the carriage 23 upwards, the carriage pivoting about the projections 22 in the-notches .21. As the end of the carriage'is forced'upwards'by the rod 36 it decreases the force in .the bi-rnetall-ic strip 24 that is tending to hold the contacts 4, 12 :open and therefore less energy is needed to be derived from the difference of expansion coeificients of the two metals constituting the bi-metal strip 24 and 'thecontacts 4, 12 will operate ata higher temperature. 7

It will be appreciated that it it is desired to have normally open contacts which closeat a higher temperature being reached this can be achieved 'by reversing the position of the bi-metal strip 24 so that it is the other way up in the switch.

. It is possible for the movable contact 12 to be carried directly. by the bi-metallic strip 24 and not by an insulating extension 31 thereof as in the construction described.

This direct attachment has the drawbacks that there'is a transmissionof heat from the contacts to the bi-metal which can cause undesirable self heating effects, and also it is-difiicultto use a back stop 17 which is deslrable in some instances such as when the switch is used inrc frigeration plant.

The type of looped jumper strap 14 described and illustrated is to be preferred to the more conventional which enables the spring 32 to be pulled over to one side or the other tolock the switch on or off at will.

Instead of the bi-metal strip carrying an electrical contact it could carry a plunger which may be arranged to operate a mechanism such as a valve for controlling a supply of fuel or for actuating tripping or indication mechanisms. a

I claim:

. 1'. A temperature responsive device comprising a body, a bimetallic strip-like element, a carriage fixed to said element at one end thereof and pivoted on said body on an axis betweent he ends of said bimetallic element and nearer said one end, a U-sha-ped spring supported by and applying a compressive force between the other end of said bimetallic element and a point on said body lying on that side .of said axis nearer said one end 'ofsaid element, and means to determine the pivotal position of said carriage.

2. A temperature responsive device comprising a body, a bimetallic strip-like element, a carriage fixed to said element at one end thereof and pivoted on said body on an axis between the ends of said bimetallic element and nearer said one end, a U-shaped spring supported by and applying a compressive iorcebetween the other endof said bimetallic element and a point on said body lying on that side of said axis nearer said one end of'said element, and means'to determine the pivotal position of said carriage, said means comprising a threaded rod, a

threaded bush mounted on said body and through which bush said rod passes and a spring engaging said body and said carriage to bias said carriage intoengagement with the end of said rod.

3. A temperature responsive device comprising a body,

applying a compressive force between the other end of said bimetallic element and a point on said body lying on that side of said axis nearer said one end of said element, means to determine the pivotal position of said carriage, and a movable electrical contact carried by the said other end of said bimetallic element and arranged to make and break contact with a fixed electrical contact.

4. A temperature responsive device comprising a body, a bimetallic strip-like element, a carriage fixed to said 7 element at one end thereof and pivoted on said body on an axis between the ends of said bimetallic element and nearer said one end, a U-shaped spring supported by and applying a compressive force between the other end of said bimetallic element and a point on said body lying on that side of said axis nearer said one end of said element, means to determine the pivotal position of said carriage, and means for adjusting the said compressive force.

5. A temperature responsive device comprising a body, a bimetallic strip-like element, a carriage fixed to said element at one end thereof and pivoted on said body on an axis between the ends of said bimetallic element and nearer said one end, a U-shaped spring supported by and applying a compresisve force between the other end of said bimetallic element and a point on said body lying on that side of said axis nearer said one end of said element, means to determine the pivotal position of said carriage, and knife edges on the parts engaged by said U-shaped spring.

6. A temperature responsive device as claimed in claim 5, wherein one of the knife edge engagements comprises a member of L-form, a knife edge on one branch of said member, an end wall of the body, a hole in said end wall from which said one branch bearing said knife edge protrudes to engage said spring, and a screw adjustably locating the other branch of said L-form member from said wall.

7. A temperature responsive device as claimed in claim 5, wherein the other knife edge is attached to the other end of the bimetallic strip.

References Cited in the file of this patent UNITED STATES PATENTS 1,734,473 Compo NOV. 5, 1929 1,845,998 Gregory Feb. 16, 1932 2,016,244 Gregory Oct. 1, 1935 2,253,553 Burch Aug. 26, 1941 2,832,869 Lenoir Apr. 29, 1958 

